Gonadotropin-dependent sexual precocity in this unique opportunity patient may be an isolated defect due to the presence of a large, pedunculated lesion of the posterior hypothalamus. This 18 month old female infant was admitted for complete evaluation of pituitary, hypothalamic, adrenal and thyroid functions, as well as neurosurgical and neurophthalamological evaluation, all of which were normal. The lesion had radiographic and MRI characteristics of a hamartoma.